In a typical wireless network, many devices can enter an area serviced by a wireless controller and communications can be set up between the devices and the controller. In state of the art systems, significant overhead features and functions are required to connect a device to a network. To facilitate an efficient set up between multiple networkable devices, communications must be effectively configured and managed. Thus, a typical wireless network has a communications coordinator or controller such as an access point, a piconet controller (PNC), or a station that configures and manages network communications. After a device connects with the controller, the device can access other networks, such as the Internet, via the controller. A PNC can be defined generally as a controller that shares a physical channel with one or more devices, such as a personal computer (PC) or a personal digital assistant (PDA), where communications between the PNC and device(s) form the network.
The Federal Communications Commission (FCC) limits the amount of power that network devices can transmit or emit. Due to the number of networks, crowded airways, requirements to accommodate more devices and the low power requirements, new wireless network standards continue to be developed. Further, it is known that the path loss for systems that transmit at 60 GHz is very high. Complimentary metallic oxide semiconductors (CMOS) are popular for manufacturing network components due to their low cost and low voltage requirements and a CMOS type power amplifier is inefficient at such frequencies. Generally, most low power 60 gigahertz (GHz) communication systems require directional beam formed systems to achieve acceptable signal to noise ratios (SNR)s and hence, acceptable communication performance.
Accordingly, there has been a lot of activity to develop low power network communications in the 60 GHz range utilizing directional communications via millimeter waves. An omni-directional transmission or communication is different from a directional transmission, as an omni-directional transmission generally has a single antenna that provides a point source of radiation. A point source has a radiation pattern where signal energy propagates evenly in a spherical manner unless obstructed by an object. In contrast, a directional communication can focus a signal or steer a signal towards a target and a receiver can focus its sensitivity or steer its sensitivity towards a source. In order to accurately steer, transmit and receive beams in the proper direction, a beamforming process or training process can be implemented between a controller and a device. To achieve directional communications several different directional transmission methods are available. One such method utilizes a sectored antenna approach, which switches signals among several predetermined beams. This method can utilize a phased antenna array where transmit and receive beams are formed by changing the phases of the input and output signals of each antenna element. Another approach distributes the transmit power to multiple power amplifiers and, based on the gain of the power amplifiers, the beam can be adaptively steered.
Beamforming is important for reliable operation of new, state of the art, high frequency low power networks. It can be appreciated that traditional omni-directional transmissions/communication topologies cannot provide reliable low power, high data rate communications at distances of over a few meters. Generally, directional antennas or antenna arrays can provide gains that are much higher than omni-directional antennas (tens of decibels). When a transmitter accurately focuses signal energy in the direction of the desired receiver and a receiver focuses it's receive sensitivity in the direction of the transmitting source, interference from other directions can be mitigated and the beamformed system will create less interference for other systems.
A directional transmission system can provide improved performance over omni-directional systems due to the increased signal strengths between devices and decreased interference from devices transmitting from directions where the receiver is less sensitive. Higher data rates, on the order of a few Gigabits per second, are possible in a directional transmission mode since the directional link benefits from higher antenna gains. However, these directional systems are typically more complex, slower to set up and more expensive than traditional omni-directional transmission systems. After an association and beam calibration process, efficient data exchange between the device, the controller and other networks, such as the Internet, can occur.
It can be appreciated that many network environments, such as offices, office buildings, airports, etc., are becoming congested at network frequencies as many devices enter a network, exit the network and move in relation to the controller of the network. Setting up directional communication and tracking movement of devices in traditional systems requires a relatively long, inefficient association time and set up time for each device. Such continued increase in the number of users for an individual network, the increase in set-up complexity and overhead continue to create significant problems.